A navigation device may be configured utilize a navigational database e.g. for calculating a route from a first location of a first region to a second location of a second region, e.g. for finding a route from Paris to Munich. The navigational database may comprise a global gateway table, which contains a list of gateways connecting adjacent update regions, and said table may associate each gateway with several update regions. The data size of the navigational database may be large, and the navigational database may be updated partially so that only one update region is modified. The partial updating may comprise downloading an update package from a server, or using an update package stored on an update medium (e.g. flash memory).
The navigational database may comprise a global gateway table, which may associate each gateway of the navigational database with an update region and with a geographical tile. The same gateway may occur in several different geographical tiles although said gateway may represent only one physical location. For example, a gateway may occur in two different layers and in two different update regions, and said gateway may occur four times in the global gateway table. The global gateway table may be updated e.g. by SQL commands when a certain update region is incrementally updated, in order to keep the global gateway table and the content of the update regions are synchronized. SQL means structured Query Language.
A navigational database for Europe may comprise e.g. 12 different update regions. Partial updating of the navigational database may comprise selecting one or more update regions from 212 different combinations of update regions. Consequently, 212 different versions of the global gateway table would be needed to match with each possible combination. A global gateway table matching with a given selection may be determined by using SQL commands, but the high number of possible alternatives may make it impractical to store the global gateway table(s) as predetermined downloadable data.